The present invention relates generally to extrusion apparatus and more particularly to an extrusion die.
Extrusion dies are used to form a desired product out of thermoplastic material. The extrusion die is fed with material at an inlet thereof and produces the desired product at an outlet. The final outlet is often described as possessing a shape that is a cross sectional profile of the final product. An important characteristic of an extrusion die is that it is used in a continuous process. This is different from molding, which is a batch process.
Flat-sheet extrusion dies typically comprise two or more die body portions that are secured together by threaded bolts. Access to the flow passages is obtained by unthreading the bolts. An example of this type of extrusion die is disclosed in commonly-assigned Wilson et al. U.S. Pat. No. 5,494,429, which describes a two-piece die body that forms a sheet of substantially uniform thickness.
Extrusion dies typically require disassembly for cleaning or maintenance of the flow passages. Extrusion dies designed for extrusion of certain types of materials can require disassembly for cleaning more than once a week. This shutting down of production can be time consuming and laborious. Disassembly typically involves unscrewing the threaded bolts that hold the die body portions together. These threaded bolts may be under high torque and difficult to remove. Unscrewing the bolts with hand tools may prove dangerous considering the tools may break off or slip injuring the operator or bystanders. Additionally, the amount of time that the extrusion die is not operating can be an economic disadvantage.
Attempts have been made in the art to speed up disassembly of various extrusion apparatus by use of clamping arrangements. For example, Coyle et al. U.S. Pat. No. 6,196,823, discloses a clamp collar assembly that clamps together an extruder and a die body at their respective peripheral surfaces. Unclamping allows for separation of the die body from the extruder to allow removal of a screen pack filter. While this arrangement is helpful for quickly changing a filter, it does not facilitate access to the flow passages of a die body.
Minuado et al. U.S. Pat. No. 5,225,208, discloses an extrusion die where rubber is co-extruded around metal wire to form tire tread plies. A clamping arrangement secures four die body plates. Two interior plates guide the wires. Two exterior plates extrude rubber onto the wires. Unclamping allows removal of the die body plates. One drawback to this arrangement is that the clamping pressure is applied by a crosspiece disposed atop the plates and clamping forces are applied to the crosspiece by pressure means attached to the ends of the crosspiece. This indirect application of clamping pressure can be less than completely effective to cause proper sealing of the die body plates.
In accordance with one aspect of the present invention, an extrusion die comprises a pair of die body portions that together define flow passages and toggle clamps that clamp the die body portions together.
In accordance with a further aspect of the present invention, an extrusion die comprises first and second die body portions that define flow passages when assembled together, a frame that holds one of the die body portions and first and second clamping rods disposed in first and second sets of passages in the die body portions, respectively. A toggling apparatus is coupled to the clamping rods and an actuator is coupled to the toggling apparatus. The actuator is operable with the toggling apparatus to move the clamping rods to a clamping position clamping the die body portions together.
In accordance with yet another aspect of the present invention, an extrusion die comprises first and second die body portions that together define flow passages, a frame that holds one of the die body portions, toggle clamps and first and second alignment pins that align the die body portions. The toggle clamps include a first plurality of clamping rods disposed in a second plurality of sets of passages in the die body portions, a third plurality of toggling linkages coupled to the first plurality of clamping rods and a fourth plurality of actuators coupled to the third plurality of toggling linkages and operable therewith to move the clamping rods to a clamping position clamping the die body portions together.
Other aspects and advantages of the present invention will become apparent upon consideration of the following detailed description.